Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Porous graphene is considered to be a desirable membrane for gas separation. Theoretical and experimental studies indicate that atom-scale holes in the graphene lattice may provide significant selectivity for separating gases based on molecular size. Further, monolayer graphene, at one atom thick, is a desirable candidate because the gas permeation rate through a membrane increases with decreasing membrane thickness.
Consequently, porous graphene membranes are being pursued for their potential to significantly outperform conventional polymeric membranes, e.g., in separating gases that are synthesized at high temperatures. For example, the “shift reaction” used to create hydrogen gas from water and carbon dioxide may run at temperatures over 400° C. Since there is currently no membrane that effectively purifies hydrogen in a single step, much less at such high temperatures, current hydrogen purification may include capital and energy intensive steps such as cooling, as well as removal of water, carbon dioxide, and other impurities.
A graphene membrane with uniformly sized pores may effectively purify hydrogen from the “shift reaction” in a single step. However, current graphene membranes having uniformly sized pores have a low membrane throughput and may be inefficient for separation when used in a two-dimensional or flat configuration. Some factors affecting the membrane throughput and efficiency of the flat graphene membranes include low probability of successful trajectory for enabling the molecule to align with and pass through a pore, a low pore area percentage, e.g. a low pore to membrane ratio, and a low gas adsorption to graphene. Some known nanofiltration methods have used porous graphene in cylindrical form for increasing the membrane throughput.